1. Field of the Invention
This invention relates to automatic/semiautomatic power transmissions providing a plurality of gear reduction ratios, such as automatic/semiautomatic mechanical transmissions (i.e. "AMTs"), and, to control systems and methods therefor. In particular, the present invention relates to control systems and methods for automatic/semiautomatic mechanical transmission systems wherein gear selection and shift decisions are made and/or executed based upon measured and/or calculated parameters such as vehicle or transmission output shaft speed, transmission input shaft speed, engine speed, throttle position, rate of change of throttle position, rate of change of vehicle and/or engine speed and the like. More particularly, the present invention relates to a control and method for controlling an AMT system including a manually operated engine compression brake during sensed vehicle deceleration by modifying the downshift logic in response to sensed throttle, vehicle brake and/or engine compression brake operation.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems utilizing discrete logic circuits and/or software controlled microprocessors for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic /semiautomatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,576,065; 4,569,255; 4,551,802; 4,527,447; 4,425,620; 4,463,427; 4,081,065; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048, 4,208,929; 4,039,061; 3,974,720; 3,478,851 and 3,942,393, and European Pat. No. 0 071,353, the disclosures of which are all hereby incorporated by reference.
Automatic control systems/subsystems for automatically controlling the engagement and disengagement of AMT system vehicle master clutches, especially during vehicle start from stop operations, are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,401,200; 4,413,714; 4,432,445, 4,509,625 and 4,576,263, the disclosures of all of which are hereby incorporated by reference.
While the above referenced automatic/semiautomatic transmission control systems, especially the system illustrated in U.S. Pat. Nos. 4,081,065; 4,361,060; 4,595,986; 4,576,065; 4,569,255 and 4,576,263, and similar systems, are effective to control the vehicle automatic/semiautomatic transmission system operations under most conditions, under certain vehicle deceleration conditions, the logic did not accurately sense vehicle operating conditions/operator intentions and some downshifts were performed in other than the most desirable manner.